Sahih Muslim Book 3, Hadith Number 643.

Chapter : Law of Shari’ah pertaining to the plaited hair of the woman who takes a bath.

Umm Salama reported: I said: Messenger of Allah, I am a woman who has closely plaited hair on my head; should I undo it for taking a bath, because of sexual intercourse? He (the Holy Prophet) said: No, it is enough for you to throw three handfuls of water on your head and then pour water over yourself, and you shall be purified.